Field of the Invention
The invention pertains to the field of timing belts and chains. More particularly, the invention pertains to a combined timing belt and timing chain.
Description of Related Art
A timing belt or chain synchronizes the rotation of the crankshaft and the camshaft in an internal combustion engine so that the engine's valves open and close at the proper times during each cylinder's intake and exhaust strokes.
Timing belts are generally thought to have a quiet and efficient operation.
Additionally, they are not known to be sensitive to contaminated oil. In a typical belt system there is a tensioning system which utilizes pulleys and bearings to guide the path of the belt and provide tension. These components do an adequate job, but they have the disadvantage of being heavy, high cost, and add parasitic loss to the system. The disadvantages to belts are their width, which required additional package space and their very abrupt failure mode which involves the belt breaking.
Timing chains are known for their high strength and long durability but some timing chains generate mechanical noise which is adverse to users. The tensioning system typically used on modern automotive chain timing systems involves the use of lightweight plastic arm and guides in which the chain moves across the surface of the plastic on an oil film resulting in a very low friction interface with corresponding very low parasitic losses. Additionally, with recent engine technology such as direct fuel injection and turbocharging, the engine oil has become more aggressive towards the chain due to contamination. This has raised questions with regards to chain wear durability.
Historically, a timing belt was not able to use a timing chain tensioning system as the materials used in belt construction were not compatible with motor oil. Recent technology advances in belt material technology have allowed a belt to be run in an environment of motor oil just like engine timing chains. Attempts were made to run a flat back belt on the surface of arms and guides used for a chain which resulted in excessive parasitic losses due to the high surface area of the belt.
There have been some chains and belts that attempt to use a combination of a chain and a belt. For example, British patent application GB 196294, which discloses a belt with outer link plates, inner link plates, sleeves and leather or belt strips. The inner link plates are connected to one another by a hard sleeve that surrounds the belt strips. The leather strips are higher than the outer link plates and the inner link plates so that the pulley is only engaged by the leather strip. The outer link plates are connected to each other by rivets, with the sleeves and the rivets forming the links of the chain. The sleeves and the rivets take both the pulling and bending strains.
U.S. Pat. No. 2,645,132 discloses a V-belt with wire chain links on either side of the upper portion of the V-belt, with connecting bars of the wire chain links passing through holes in the upper portion of the V-belt.
German patent DE 33 47 957 C2 discloses a double stranded belt with rigid teeth connected by pins. Pins and lugs pass through the centers of the double stranded belt.
Most of the other combinations present the chain within an interior of a belt. For example, U.S. Pat. No. 2,113,790 discloses a chain that has two flexible drive belts present on the outside of the chain. U.S. Pat. No. 2,555,190 discloses a V-belt with a wire chain within the belt to reinforce the V-belt. U.S. Pat. No. 2,224,068 discloses a chain surrounded by V-belts on either side. Swedish application SE 113793 discloses a belt with a rubber body with a core of a roller chain.